1. Field of the Invention
The present invention relates to an electrophotographic type fixing device, an image forming apparatus and a surface restoration method.
2. Description of Related Art
In general, an electrophotographic image forming apparatus (such as a printer, a copy machine, and a fax machine) is configured to irradiate (expose) a charged photoconductor with (to) laser light based on image data to form an electrostatic latent image on the surface of the photoconductor. The electrostatic latent image is then visualized by supplying toner from a developing device to the photoconductor (image carrier) on which the electrostatic latent image is formed, whereby a toner image is formed. Further, the toner image is directly or indirectly transferred to a sheet, followed by heating and pressurization, whereby an image is formed on the sheet.
An example of the fixing device that fixes a toner image in the above-mentioned manner is a heat-fixing type fixing device that applies heat and pressure on a sheet on which a toner image has been transferred while passing the sheet through a fixing nip formed by a fixing side member such as a fixing roller or a fixing belt and by a back side supporting member such as a pressure roller or a pressing belt which is brought into pressure contact with the fixing side member.
There is known a problem that, when a thick sheet or a sheet having a rough surface is passed through the fixing nip, a sheet-edge mark is left on the surface of the fixing side member, at a position which makes contact with the both end portions of the sheet. When forming an image having an image forming range including the position where the sheet-edge mark is left, the fixing process is not uniformly performed in the sheet width direction because of the sheet-edge mark, resulting in gloss unevenness in the fixed image. To be more specific, the glossiness of the image which has been fixed at the position where the sheet-edge mark is left becomes lower than the glossiness of the image which is formed at the position where the sheet-edge mark is not left.
In order to solve the above-mentioned problem, Japanese Patent Application Laid-Open No. 2010-217466 discloses a technique in which, at a nip portion, a speed difference is provided between a fixing member (fixing side member) and a pressing member (back side supporting member), and the two members are brought into sliding contact with each other to thereby perform cleaning on the surfaces of the fixing side member and the back side supporting member.
In addition, Japanese Patent Application Laid-Open No. 2008-20790 discloses a technique in which a restoring section (refreshing roller) that restores the surface property of a fixing roller (fixing side member) to improve the fixing performance is provided.
However, with the technique of Japanese Patent Application Laid-Open No. 2010-217466, depending on the state of the fixing nip formed between the fixing side member and the back side supporting member, the surface of the fixing side member and the surface of the back side supporting member may not slip smoothly, and consequently the fixing side member and the back side supporting member may not be rotationally driven with the desired speed difference therebetween. In this case, since sufficient rubbing between the fixing side member and the back side supporting member is not achieved, the sheet-edge mark left on the fixing side member may not be removed, and gloss unevenness due to the sheet-edge mark may not be surely prevented.
With the technique disclosed in Japanese Patent Application Laid-Open No. 2008-20790, a dedicated device for restoring the surface property of the fixing side member has to be separately provided, and therefore the cost of the fixing device may be increased.